Long a companion for artists, the color wheel can also be a handy tool for gardeners.

Gardening author Sydney Eddison created a wheel that has 252 colors instead of the usual 12. That's because nature doesn't work with a limited palette, she says.

"In nature you have already been dealt this hand. You only have to learn how to play it," she says.

Even all of the tints, shades and tones in Eddison's "The Gardener's Color Wheel" don't capture the diversity of what's really growing out there. But she says it's a good way to start seeing colors in the garden and how they relate to each other.

"The color wheel trains your eye to look, to really look," says Eddison, author of six books including "The Gardener's Palette" (Contemporary Books, 2003). "You begin to understand why certain things work, or why you like a Christmas wreath that's red and green and why you're happy to see purple and yellow crocuses together."

In both examples, the two colors are complementary — opposite each other on the color wheel — and in color theory, opposites attract.

In garden planning, colors are used to create either contrast or harmony, says Eddison, who has tended 2½ acres in Newtown, Conn., for half a century.

"Contrast calls attention to itself. It gives a jolt," says Eddison, 81. "Whereas harmony is a sigh of relief."

Colors adjacent on the color wheel, such as the warm shades of red and orange or the cool tones of blue and green, create harmony together.

Take a color wheel into the yard to parse out particular colors. Take it to the garden center to help pick out plants for the summer.

Then play in the soil.

Eddison recommends experimenting with color in pots on the terrace.

"Don't force a color theme on the garden," she warns. "It has different colors at different times of the year."

Color also changes throughout the day, depending on the light.

Eddison changes her patio pots every year, and paints her garden furniture to coordinate.

"Sometimes my color schemes are a little wild I had a Crayola color scheme one year," she says. "People were blinded by it, but I loved it."

"The year that I did yellow, white and yellow-green, that was terrific," Eddison says. "And I painted the furniture yellow."

Look to fabrics or famous artwork (Monet's paintings, for example) for color inspiration, she suggests.

Or simply trust nature, which turns out complementary color combinations all its own, says Betina Fink, an oil painter who teaches color theory in Tucson, Ariz.

"There are these beautiful, naturally occurring complementary colors," she says. During spring in the Southwest, for example, prickly pear cacti sport buds and blooms ranging from yellows to purples.

When planning a garden, remember that cool colors, such as blues and violets, recede, says Fink. Warm colors — reds, oranges and yellows — want to take center stage. Green — nature's most abundant color in many places — is "the great peacemaker," says Eddison.

An incompatible color scheme can be softened by incorporating more soothing green foliage. In particular, gray and gray-green foliage helps blend colors.

Meanwhile, a little white goes a long way in the garden, warns Eddison.

"It is the lightest and brightest and most eye-catching color in the garden," she says. "It requires special handling."

White works well with individual colors or combined with pastels. Low-growing white flowers, such as the tickseed plant "Star Cluster" Coreopsis, when spread throughout a garden can help the eye scan its surroundings.

Flowers come and go, but foliage often remains year-round, so plan it carefully, says Webber. She likes orange foliage, a relative newcomer, and mentions the perennial Heuchera Marmalade, a variety of coral bells.

Instead of hard and fast rules, Webber trusts her eyes to know when two plant colors clash: A bad combination hurts. "If I'm cheating and putting colors together that don't go well together, I'll see how my eyes are feeling," she says.

Over decades of experimenting with color, Eddison also has found that rules can only get a gardener so far.

"As much as following the rules works, ditch them to follow your heart and soul," she says.

Eddison's color wheel and instructional booklet may be purchased from the publisher, The Color Wheel Co. in Philomath, Ore., online for $15. The booklet's cover depicts a floral wreath created by Webber that emulates a color wheel.